1. Field of the Invention
This invention relates to a hybrid microturbine engine having a 1st and 2nd rotor spool and a turbo charged multistage compressor system where one rotor spool incorporates a turbine and compressor as the turbo charger and the 2nd spool having a turbine, compressor, and an alternator rotor in close proximity and co-axially within a laminated iron base stator having wires to generate electricity.
2. Description of Prior Art
It can be appreciated that microturbine devices have been in use for years. Typically, a microturbine device is comprised of a single rotor spool with integral alternator attached and used in distributed electrical power generation. Companies include Elliott Energy Systems (EES), Turbec, Honeywell (some development effort only then bought out by GE) and Capstone with a wrap around heat exchanger was applied to a bus transport vehicle in a DOE power development program for low emissions considerations. Turbec/Volvo's VT100 microturbine with its external heat exchanger was tested in a bus transport application with low emissions and this engine became the base for Turbec's more recent effort of distributed electrical power applications. EES has not directed any effort toward vehicular applications. Currently the single spool microturbines are being used exclusively in a main or emergency electrical power source for distributed power generation with multifuel, low emission capability and higher durability compared to the piston type engines. Companies world wide have attempted to incorporate a gas turbine engines prior to the microturbines into vehicular applications since ˜1950. Vehicular gas turbines have been designed and tested since 1950 with the initial idea from Mr. Huebner of GM in 1938. Typically gas turbine engines similar to piston engines tested in vehicles, operate most of the time <38% of the total capable engine power and is therefore important to have good part power efficiency for low fuel consumption. Many companies have attempted to implement gas turbine engines for main power into production vehicles thru design and test and include: Energy Transfer Co., Williams International, UTRC, PWA, GE, Kawasaki, US Army, NASA, Allison, US DOT-DOE, Volvo/United Turbine/KTT, ABB/Turbec, M.A.N., Volkeswagon, Mercedes, NREC, Concepts, MIT (also other universities), Brown and Boveri, Chrysler, Rover, Rolls Royce, Honda, Allied Signal/Garrett, Ford and GM. Avco Lycoming had successfully implemented the AGT 1500 gas turbine into the Abrams M1 tank and is currently used today. This is a two spool engine having a compressor pressure ratio>16:1, a free turbine for output power and a recuperator heat exchanger is incorporated for reduced power fuel efficiency gains. Most recently Capstone Turbine Corp. with its microturbine bus application reflect good low emissions.
Limited use is due to high total system cost, durability of the heat exchanger and air bearings not suitable for vehicle road travel with related G forces and clean air supply to the air bearings. Typical earlier prior art selected automotive power was less than 140 HP and 250 to 600 HP range for trucks or heavy equipment. The engines on the part comprised of <5:1 compressor ratio, mechanical gear boxes, electrical starting thru a gear box and a form of gas-hear recovery system which included either a recuperator (large weighty device) and limited to <1300 F inlet temperature or a ceramic type regenerator. Engine designs have incorporated (1) or (2) rotor[/]spools (a compressor/turbine rotor assembly), gear boxes and in some applications a free turbine making a three spool system like KTT. Engine speeds were usually near design conditions to avoid lower RPM critical shaft speed vibration issues and or blade frequency issues, requiring a means of governing output engine power thru air flow control thus lacking in part power fuel economy optimization if without a heat exchanger device. Ceramic materials for use in the hot turbine section offer improved engine fuel efficiency thru higher turbine inlet temperatures (2500 F) but material durability has been an issue. Extensive development in various countries since 1970 and to date have not yielded durable ceramic components for vehicle gas turbine integration. A target of 2500 F turbine inlet temperature (TIT) has been a goal to improve thermal efficiency, but higher combustor flame temperature will yield higher NOx with hydrocarbon fuel and air use and will need further combustor considerations. Correspondingly nickel/cobalt alloy turbine materials with (TIT)<1875 F have been predominately used and non cooled, for cost considerations although industry has proposed ˜2000 F. Gas turbines continue to be of interest for various applications including vehicles for low emissions (without catalytic treatment), low weight, compactness, low maintenance, multi-fuel capability, no vibration and high engine durability as compared to the piston type power-plants which are designed to wear-out. Most recent gas turbine single spool microturbines have incorporated non synchronous high speed alternators with permanent magnets to the compressor/turbine rotor spool per initiating U.S. Pat. No. 6,314,717 offering reduced cost and simplicity. The Adkin U.S. Pat. No. 3,187,180 first implemented a generator rotor integration with a gas turbine engine removing the need for gearbox complexity and allowing for the first time frequency control independent of RPM engine speed; but power electronics remained costly and technology elusive to change high frequency and voltage to 60 HZ@ 110 or 220 volts as an example. The U.S. Pat. No. 6,314,717 patent further introduced a low cost, low emissions single spool gas turbine with affordable available technology and power electronics yielding the first low cost electrical power generation system. Exclusively, to date small gas turbines <500 HP (not microturbines) have been used in auxiliary power units (APU) with constant speed generators or air cycle machines all incorporating gearboxes and used as ground base gen-sets or in aircraft. The prior microturbine applications are toward maximum power levels in stationary electrical power needs with a total system cost too high for vehicular applications as well as specific start/shutdown cycle to maximize heat exchanger mechanical stress/life. The total system installation cost of less the $1000/KW was a target and less the $500/KW as a simple cycle associated (no recuperator) gas turbine was attained in an engine <100 kw had been demonstrated but without a heat exchanger included with a single spool concept. However, high fuel use would be prohibitive for continuous operation if fuel cost is an issue. Electrically starting the microturbine using the alternator has been introduced replacing the related gearbox needs but may be electronically too complex and cost prohibitive <250 KW engine due to power electronic hardware cost. With the advent of microturbines for electrical power generation, the vehicular application could be implemented with further engine system package “adjustment”. The current vehicular power-train components like the transmission could be replaced with an electric motor.
The main problems with conventional microturbine devices for large scale usage are cost of the power electronics start system and the related heat exchanger. Considering the Capstone microturbine engine in a demonstrator vehicular application, although exhibited improved low emissions and reduced cost over the earlier prior art engine with gear box complexity, the system/package initial purchase cost is still an issue of high cost. Another problem with conventional microturbine devices are durability, although better than the piston type internal combustion engines, it needs improvement to further off-set the initial system expense thru reduced maintenance costs. The prior art microturbine applications are toward max power levels stationary electrical power needs and the total system cost is too high for vehicular applications. One of the main issues is to remove the costly heat exchanger and have the ability to reduce the rotor speed at off design maximum power to reduce fuel usage with the reduced compressor pressure ratio needs at lower rotor speeds. With the reduced engine rotor speed capability both rotor dynamic and component natural frequency need to be addressed. Another problem with conventional microturbine devices are performance. Need to have fuel economy to be 30 to 50% better than a piston engine is a 75 kw class engine and acceleration capability of 0 to 60 mph in <15 seconds minimum, have been requirements per Ford during the late 70's development program with the Garrett engine company. During these earlier tests, a 20% fuel economy improvement had been attained but the acceleration tests were marginal. Although a good high effective recuperator >90% has been experienced in a microturbine to yield good fuel economy (>29% cycle efficiency and better than conventional piston engine) durability is an issue. Also, during reduced power engine requirements, off loading from a high power levels using a current microturbine, the combustor flame stability will be an issue because of the initial stored heat energy in the recuperator device. The rotor system, with related rotor dynamics and or blade frequency could be of issue at reduced speed if not designed properly. The fuel control system may become complex and emissions be an issue during the engine transient operation using the current microturbines. In prior art the microturbine had controlled the engine power with fuel supply maintaining the engine at a constant or small range of engine speed and simultaneously varying the fuel flow level thus avoiding any rotor dynamic and or rotor spool-up lag issues. While these microturbine devices may be suitable for the particular purpose to which they address, they are not as suitable for providing electrical power generation for vehicular application. This new invention of a hybrid microturbine could also be used for non-vehicular application like the current microturbine. In these respects, the hybrid microturbine having a 1st and 2nd rotor spool, a turbo charged multistage compressor system, an integral alternator rotor with a close proximity stator wire/laminat system and a turbine to generate electricity according to the present invention substantially departs from the conventional concepts and designs of the prior art.